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Abstract:

A process for producing a foamed blow-molded article, including melting
and mixing a branched polycarbonate resin having a specific polystyrene
equivalent weight average molecular weight, a specific weight average
absolute molecular weight and a relatively high terminal hydroxyl group
content, a linear polycarbonate resin having specific polystyrene
equivalent weight average molecular weight, a specific weight average
absolute molecular weight and a relatively low terminal hydroxyl group
content and a branching agent to obtain a polycarbonate resin "A", mixing
the polycarbonate resin "A" with a blowing agent to obtain a foamable
molten resin composition, extruding the foamable molten resin composition
to obtain a foamed parison, and blow-molding the foamed parison.

Claims:

1. A process for producing a polycarbonate resin foamed blow-molded
article, comprising the steps of (a) melting and mixing a branched
polycarbonate resin "B", a linear polycarbonate resin "C" and a branching
agent "D" to obtain a polycarbonate resin "A" in a molten state, wherein
the branched polycarbonate resin "B" has a polystyrene equivalent weight
average molecular weight MwB(PS) of 5.5.times.10.sup.4 to
7.0.times.10.sup.4, a weight average absolute molecular weight
MwB(abs) providing a ratio MwB(abs)/MwB(PS) of the weight
average absolute molecular weight MwB(abs) to the weight average
molecular weight MwB(PS) of 0.63 to 0.70 and a content of terminal
hydroxyl groups of 500 ppm by mass or more, and the linear polycarbonate
resin "C" has a polystyrene equivalent weight average molecular weight
MwC(PS) of less than 5.0.times.10.sup.4, a weight average absolute
molecular weight MwC(abs) providing a ratio MwC
(abs)/MwC(PS) of the weight average absolute molecular weight
MwC(abs) to the weight average molecular weight MwC(PS) of 0.62
or less and a content of terminal hydroxyl groups of 250 ppm by mass or
less, and wherein the branched polycarbonate resin "B" and the linear
polycarbonate resin "C" are used in such a proportion as to provide a
mass ratio B:C of the branched polycarbonate resin "B" to the linear
polycarbonate resin "C" of 30:70 to 95:5, (b) mixing the polycarbonate
resin "A" in a molten state with a blowing agent to obtain a foamable
molten resin composition, (c) extruding the foamable molten resin
composition to obtain a foamed parison, and (d) blow-molding the foamed
parison to obtain a foamed blow-molded article.

2. The process according to claim 1, wherein the foamed parison has a
polystyrene equivalent weight average molecular weight MwF(PS) of
5.0.times.10.sup.4 to 10.times.10.sup.4, and a weight average absolute
molecular weight MwF(abs) providing a ratio
MwF(abs)/MwF(PS) of the weight average absolute molecular
weight MwF(abs) to the weight average molecular weight MwF(PS)
of 1.0 or more.

3. The process according to claim 1, wherein the branching agent D is an
epoxy-functional acrylic polymer that has a weight average molecular
weight of 5,000 to 20,000 and an epoxy value of 1.5 meq/g or more.

4. The process according to claim 3, wherein, in step (a), the branching
agent D is used in an amount of 0.5 to 4.5 parts by mass per 100 parts by
mass of the branched polycarbonate resin "B".

5. The process according to claim 1, wherein the blowing agent is an
inorganic physical blowing agent.

6. A polycarbonate resin hollow foamed blow-molded article having a
polystyrene equivalent weight average molecular weight MwF(PS) of
5.0.times.10.sup.4 to 10.times.10.sup.4, and a weight average absolute
molecular weight MwF(abs) providing a ratio
MwF(abs)/MwF(PS) of the weight average absolute molecular
weight MwF(abs) to the weight average molecular weight MwF(PS)
of 1.0 or more, said hollow foamed blow-molded article having an apparent
density of 0.1 to 0.8 g/cm3, an average thickness of 0.5 to 10 mm
and a closed cell content of 60% or more.

[0003] The present invention relates to a process for producing a
polycarbonate resin foamed blow-molded article by blow molding a foamed
parison, and to a polycarbonate resin foamed blow-molded article.

[0004] 2. Description of Prior Art

[0005] Because a polycarbonate resin (hereinafter occasionally referred to
as "PC resin") has much higher melt viscosity at near its foaming
temperature and requires an extremely higher extrusion pressure as
compared with other resins such as polystyrene, it has been difficult to
extrude and foam the PC resin. Moreover, because the melt tension of a PC
resin is much smaller than other resins such as polystyrene, cells are
apt to be broken during the growth thereof. Therefore, the obtained PC
resin extruded foamed product shows only an insufficient expansion ratio
and the cells thereof are not uniform in size. In particular, the PC
resin foamed blow-molded article has an expansion ratio of as low as
about 1.3. It has not been possible to obtain a PC resin foamed
blow-molded article having such a high expansion ratio as achieved in the
case of a polystyrene or a polyethylene resin.

[0006] In this circumstance, Japanese unexamined patent publication No.
JP-A-2000-033643 proposes a method in which a PC resin having a branched
structure and a specific melt tension is extruded to form a foamed
parison. By blow-molding the parison, a PC resin foamed blow-molded
article having an acceptable expansion ratio is obtainable.

[0007] Japanese unexamined patent publication No. JP-A-2008-144084
proposes a method in which a modified PC resin obtained by modifying a
commercially available branched PC resin with a branching agent is
extruded through a die with a large area to obtain a foamed board that
has a high expansion ratio and a large sectional area and that shows a
high compression strength even at both side end regions in the width
direction thereof.

SUMMARY OF THE INVENTION

[0008] With the method proposed in JP-A-2000-033643, however, it has been
found that the closed cell content of the foamed blow-molded article
tends to decrease and the wall thickness thereof tends to be non-uniform
when an attempt is made to further increase the expansion ratio thereof,
further decrease the wall thickness thereof or further reduce the cell
size thereof. Thus, there remains a room for further improvement in
producing excellent foamed blow-molded articles. It has also been found
that the method proposed in JP-A-2008-144084 is not applicable to the
production of a foamed blow-molded article. Namely, the modified PC resin
has so high a melt viscosity that it is not possible to form a foamed
parison suitable for blow molding.

[0009] It is an object of the present invention to provide a process for
producing a PC resin foamed blow-molded article that has a high closed
cell content irrespective of whether its apparent density is high or low
(in other words, irrespective of whether its expansion ratio is low or
high).

[0010] It has been found that the above-described problems can be solved
by extruding a foamable molten resin composition containing, as a base
resin, a specific PC resin to form a foamed parison and blow-molding the
foamed parison. The present invention has been completed based on the
above finding.

[0011] In accordance with a first aspect of the present invention, there
is provided a process for producing a polycarbonate resin foamed
blow-molded article, comprising the steps of:

[0012] (a) melting and mixing a branched polycarbonate resin "B", a linear
polycarbonate resin "C" and a branching agent "D" to obtain a
polycarbonate resin "A" in a molten state,

wherein the branched polycarbonate resin "B" has a polystyrene equivalent
weight average molecular weight MwB(PS) of 5.5×104 to
7.0×104, a weight average absolute molecular weight
MwB(abs) providing a ratio MwB(abs)/MwB(PS) of the weight
average absolute molecular weight MwB(abs) to the weight average
molecular weight MwB(PS) of 0.63 to 0.70 and a content of terminal
hydroxyl groups of 500 ppm by mass or more, and the linear polycarbonate
resin "C" has a polystyrene equivalent weight average molecular weight
MwC(PS) of less than 5.0×104, a weight average absolute
molecular weight MwC(abs) providing a ratio
MwC(abs)/MwC(PS) of the weight average absolute molecular
weight MwC(abs) to the weight average molecular weight MwC(PS)
of 0.62 or less and a content of terminal hydroxyl groups of 250 ppm by
mass or less, and wherein the branched polycarbonate resin "B" and the
linear polycarbonate resin "C" are used in such a proportion as to
provide a mass ratio B:C of the branched polycarbonate resin "B" to the
linear polycarbonate resin "C" of 30:70 to 95:5,

[0013] (b) mixing the polycarbonate resin "A" in a molten state with a
blowing agent to obtain a foamable molten resin composition,

The above step (b) may be preceded by or simultaneous with the step (a).

[0016] In a second aspect, the present invention provides the process
according to the above first aspect, wherein the foamed parison has a
polystyrene equivalent weight average molecular weight MwF(PS) of
5.0×104 to 10×104, and a weight average absolute
molecular weight MwF(abs) providing a ratio
MwF(abs)/MwF(PS) of the weight average absolute molecular
weight MwF(abs) to the weight average molecular weight MwF(PS)
of 1.0 or more. In a third aspect, the present invention provides the
process according to the above first or second aspect, wherein the
branching agent D is an epoxy-functional acrylic polymer that has a
weight average molecular weight of 5,000 to 20,000 and an epoxy value of
1.5 meq/g or more. In a fourth aspect, the present invention provides the
process according to the above third aspect, wherein, in step (a), the
branching agent D is used in an amount of 0.5 to 4.5 parts by mass per
100 parts by mass of the branched polycarbonate resin "B". In a fifth
aspect, the present invention provides the process according to any one
of the above first to fourth aspects, wherein the blowing agent is an
inorganic physical blowing agent. In a sixth aspect, the present
invention provides a polycarbonate resin hollow foamed blow-molded
article having a polystyrene equivalent weight average molecular weight
MwF(PS) of 5.0×104 to 10×104, and a weight
average absolute molecular weight MwF(abs) providing a ratio
MwF(abs)/MwF(PS) of the weight average absolute molecular
weight MwF(abs) to the weight average molecular weight MwF(PS)
of 1.0 or more, said hollow foamed blow-molded article having an apparent
density of 0.1 to 0.8 g/cm3, an average thickness of 0.5 to 10 mm
and a closed cell content of 60% or more. In a seventh aspect, the
present invention provides the polycarbonate resin hollow foamed
blow-molded article according to the above sixth aspect, wherein the
hollow foamed blow-molded article has a thickness variation coefficient
Cv of 50% or less. In an eighth aspect, the present invention
provides the polycarbonate resin hollow foamed blow-molded article
according to the above sixth or seventh aspect, wherein the hollow foamed
blow-molded article has an average cell diameter of 0.1 to 1 mm.

[0017] In the process according to the present invention, a foamable
molten resin composition containing a specific PC resin "A" and a blowing
agent is extruded to obtain a foamed parison in a softened state, which
is then blow-molded to obtain a PC resin foamed blow-molded article
(hereinafter occasionally referred to as "foamed blow-molded article").
The PC resin "A" is a product obtained by melting and kneading a branched
PC resin "B" having a relatively high content of terminal hydroxyl
groups, a linear PC resin "C" having a relatively low content of terminal
hydroxyl groups and a branching agent D, wherein the PC resins "B" and
"C" are present in a specific ratio. By using the specific PC resin "A",
improved foamability and blow-moldability can be achieved without any
substantial adverse affect on the mechanical strength and formability
that are inherent to PC resin. Therefore, it is possible to obtain a
foamed blow-molded article that has a high closed cell content, excellent
uniformity in the wall thickness and excellent surface appearance
throughout a wide range of its apparent density. Thus, the foamed
blow-molded article obtained by the process of the present invention has
excellent mechanical strengths such as bending strength and impact
resistance despite its light weight and also shows excellent heat
resistance and cold impact resistance that are inherent to the PC resin
and, therefore, may be advantageously used for various applications such
as automobile parts, electric or electronic parts and receptacles.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0018] In a preferred embodiment of the process of the present invention,
PC resin "A" is melted and kneaded together with a blowing agent in an
extruder to form a foamable molten resin composition. The molten resin
composition is extruded through a die to obtain a foamed parison in a
softened state. The parison is inserted between molds and a compressed
gas such as air, called blow air, is blown into the parison to expand the
parison so that the outer surface of the parison is pressed against the
inside wall of the molds. Thus, the foamed parison is blow-molded to
obtain a hollow foamed blow-molded article having a shape conforming to
the shape of the mold.

[0019] More particularly, the process for producing a polycarbonate resin
foamed blow-molded article includes the steps of

[0020] (a) melting and mixing a branched polycarbonate resin "B", a linear
polycarbonate resin "C" and a branching agent "D" to obtain a
polycarbonate resin "A" in a molten state,

[0021] (b) mixing the polycarbonate resin "A" in a molten state with a
blowing agent to obtain a foamable molten resin composition,

[0023] (d) blow-molding the foamed parison to obtain a foamed blow-molded
article. Namely, the formable molten resin composition obtained in step
(b) contains PC resin "A" that is produced by melting and kneading a
branched PC resin "B" having a relatively high content of terminal
hydroxyl groups, a linear PC resin "C" having a relatively low content of
terminal hydroxyl groups and a low melt viscosity and a branching agent
D, wherein PC resins "B" and "C" are present in a specific ratio (step
(a)). By extruding the formable molten resin composition (step (c)), it
is possible to prevent breakage of cells during foaming and to obtain a
foamed parison having a closed cell structure. Further, such a closed
cell structure of the foamed parison is maintained throughout the period
during which the foamed parison is in a molten state, or until it has
been placed between molds. Moreover, the closed cell structure is still
maintained during the course of the blow molding (step (d)). Thus, it is
possible to obtain a blow-molded article having a high closed cell
content even when the apparent density thereof is low and even when the
cell size thereof is made smaller than that of the conventional PC resin
foamed blow-molded article. Furthermore, the process of the present
invention makes it possible to produce a blow-molded article having good
surface appearance.

[0024] The process of the present invention in which a specific PC resin
is used enables the formation of a foamed parison which has improved
foamability and blow moldability. The reasons for this are considered as
follows. In a foam blow molding process, it is essential to form a foamed
parison that is in a good foaming state and capable of being uniformly
drawn during the blow molding stage in order to obtain a blow-molded
article having a high closed cell content and uniform wall thickness.
Formation of a foamed parison requires extrusion of a foamable molten
resin composition through a die having a small clearance within a short
period of time at a temperature that is suited for foaming. It is,
therefore, necessary that such a formable molten resin composition not
only shows such fluidity that permits extrusion thereof within a short
period of time at a temperature suited for foaming, but also has melt
tension sufficient for preventing the cells of the foamed parison from
being destroyed throughout the foaming and blow molding stages.

[0025] In actual, however, no PC resins have been hitherto known that can
give such a formable molten resin composition. For example, as a PC resin
having a high melt tension, a branched PC resin in which branches are
formed in its polymerization stage is commercially available. By forming
a foamed parison using such a PC resin having a specific melt tension, it
is possible to obtain a foamed blow-molded article having a relatively
high expansion ratio. With this technique, however, it has been found
that the closed cell content of the foamed blow-molded article tends to
decrease and the wall thickness thereof tends to be non-uniform when an
attempt is made to further increase the expansion ratio thereof, further
decrease the wall thickness thereof or further reduce the cell size
thereof. Thus, there remains a room for further improvement in producing
excellent foamed blow-molded articles. As a means for preventing cell
breakage during foaming and blow molding stages, a thought may occur to
further improve the melt tension of a PC resin by further branching the
PC resin. Although a highly branched structure is able to be introduced
into a branched PC resin for increasing the melt tension thereof by
modifying the branched PC resin with a branching agent, it has been found
that such a highly branched PC resin has so high a molecular weight (melt
viscosity) that it is difficult to extrude the foamable molten resin
composition at a proper foaming temperature. Additionally, when an
intermittent extrusion using an accumulator is adopted for foam blow
molding, it becomes further difficult to extrude such a highly branched
PC resin, because dependency of the melt viscosity thereof upon shear
rate is so high that the melt viscosity in a low shear rate (at the time
the supply from the accumulator has started) is very high. In this case,
although a foamed parison could be formed by increasing the resin
temperature above the proper resin temperature, the blow moldability of
the obtained foamed parison so poor that the wall thickness of the
obtained foamed blow-molded article becomes non-uniform and the surface
appearance becomes also deteriorated.

[0026] In the process of the present invention, the formable molten resin
composition, which contains a blowing agent and a PC resin "A" that is
obtained by melting and kneading a branched PC resin "B" having a
relatively high content of terminal hydroxyl groups, a linear PC resin
"C" having a relatively low content of terminal hydroxyl groups and a low
viscosity, and a branching agent D, is extruded to form a foamed parison
which is then blow-molded to obtain a foamed blow-molded article having a
high closed cell content and good surface appearance.

[0027] Although not wishing to be bound by the theory, it is inferred that
the improvement in foamability and blow-moldability of PC resin "A" is
achieved for the following reasons. Namely, when a branched PC resin "B"
having a relatively high content of terminal hydroxyl groups, a linear PC
resin "C" having a relatively low content of terminal hydroxyl groups,
and a branching agent "D" are melted and mixed together, a PC resin "B"
is considered to react with the branching agent "D" so that the PC resin
"B" is further branched to form a highly branched PC resin having a
reduced free volume and increased dependency of its melt viscosity upon
shear rate. The linear PC resin "C" which has a relatively low content of
terminal hydroxyl groups, on the other hand, does not or almost does not
react with the branching agent "D" and remains as such in the molten
kneaded mixture. Thus, it is considered that the PC resin "A" is in the
form of a mixture that includes the highly branched PC resin "B" formed
by reaction with the branching agent "D" and the linear PC resin "C"
having a relatively low viscosity. As a consequence, the mixture (i.e. PC
resin "A") not only exhibits a high melt tension, which is attributed to
the highly branched PC resin "B", but also has a high fluidity and a low
tendency to change its melt viscosity under high and low shear rates,
which are attributed to the linear PC resin "C". For this reason, the
foamed parison obtained from PC resin "A" is considered to be capable of
achieving improvement in foamability and blow-moldability.

[0028] As used herein the term "polycarbonate resin" refers to a polyester
of carbonic acid and a glycol or a dihydric phenol. The polycarbonate
resin is preferably an aromatic polycarbonate resin that is derived from
a bisphenol such as 2,2-bis(4-oxyphenyl)propane (Bisphenol A),
2,2-bis(4-oxyphenyl)butane, 1,1-bis(4-oxyphenyl)cyclohexane,
1,1-bis(4-oxyphenyl)isobutane and 1,1-bis(4-oxyphenyl)ethane.

[0029] The weight average molecular weight of a PC resin may be determined
by gel permeation chromatography (hereinafter referred to as GPC for
brevity) using ultraviolet spectrophotometer (UV) as a detector. Such a
weight average molecular weight is an equivalent value calibrated using a
standard polymer with known molecular weight. When linear polystyrene is
used as the standard polymer, the determined weight average molecular
weight of the PC resin is a polystyrene equivalent weight average
molecular weight (hereinafter occasionally referred to as Mw(PS)). The
molecular weight Mw(PS) serves as an index for fluidity of the PC resin
in a molten state but does not reflect the real molecular weight thereof.
For example, when the PC resin has a branched structure, the Mw(PS) value
becomes relatively small. On the other hand, the weight average absolute
molecular weight (hereinafter occasionally referred to as Mw(abs)) of a
PC resin represents the real molecular weight thereof. Therefore, the
higher the branching degree of a PC resin, the greater is the
Mw(abs)/Mw(PS) value thereof.

[0030] A weight average absolute molecular weight of a polymer may be
measured using a detector system including a differential refractometer,
a light scattering detector and, if necessary, a viscometer. The light
scattering technique utilizes Rayleigh scattering of a solution of the
polymer irradiated with a laser light. The intensity of scattered light
is measured. The obtained data are plotted (Debye plot). When
KC/R(θ) is plotted on the y-axis and sin2(θ/2) is
plotted on the x-axis, a linear relationship is obtained. Here, K
represents optical constant, C represents the polymer concentration and
R(θ) represents the relative intensity of the scattered light at
scattering angle θ. The weight average absolute molecular weight
Mw(abs) is able to be determined from the intercept point on the y-axis.
There are three types of light scattering detectors; i.e. low angle laser
light scattering detector (LALLS), right angle laser light scattering
detector (RALLS) and multi angle laser light scattering detector (MALLS).
In the present invention, the weight average absolute molecular weight
Mw(abs) is measured by analysis method using GPC coupled with RALLS.

[0031] In the present invention, the weight average absolute molecular
weight Mw(abs) and polystyrene equivalent weight average molecular weight
Mw(PS) may be determined by using the measurement devices and measurement
conditions as exemplified below. The polystyrene equivalent weight
average molecular weight Mw(PS) is measured using a UV spectrophotometer
detector, while the weight average absolute molecular weight Mw(abs) is
measured by using a triple detector system composed of a differential
refractive index detector, RALLS and a differential pressure viscometer
detector. GPC device:

[0045] The branched PC resin "B" must have a polystyrene equivalent weight
average molecular weight MwB(PS) of 5.5×104 to
7.0×104. When MwB(PS) is within the above range, the
weight average molecular weight of the molten PC resin "A" to be extruded
falls within the range that is suitable for foam blow molding while the
branching degree of thereof is maintained in a high degree. From this
point of view, the molecular weight MwB(PS) is preferably
5.5×104 to 6.8×104, more preferably
5.5×104 to 6.5×104.

[0046] The branched PC resin "B" must also have a ratio
MwB(abs)/MwB(PS) of 0.63 to 0.70, where MwB(abs)
represents a weight average absolute molecular weight of the branched PC
resin "B" and MwB(PS) is as defined above, in order to achieve the
objects of the present invention. The higher the
MwB(abs)/MwB(PS) ratio (this ratio will be hereinafter
occasionally referred to as "branching degree B"), the greater is the
number of branches of the PC resin "B". The branching degree B is
preferably 0.65 or more.

[0047] It is important that the linear PC resin "C" should have a
polystyrene equivalent weight average molecular weight MwC(PS) of
less than 5.0×104 in order to produce a foamed blow-molded
article having a high closed cell content and a good appearance. By
incorporating the linear PC resin "C" in the PC resin "A", it is possible
to reduce the melt viscosity of the PC resin "A" and to decrease a melt
viscosity change thereof under high and low shear rates, while
maintaining its excellent foamability attributed to the PC resin "B" that
is modified by the branching agent "D". The high closed cell content of
the obtained foamed blow-molded article is considered to be achieved for
this reason. From this point of view, the molecular weight MwC(PS)
is preferably 3.0×104 to 4.5×104, more preferably
3.0×104 to 4.0×104.

[0048] It is also important that the linear PC resin "C" should have a
ratio MwC(abs)/MwC(PS) of 0.62 or less, where MwC(abs) is
a weight average absolute molecular weight of the linear PC resin "C" and
MwC(PS) is as defined above, in order to achieve the objects of the
present invention. The smaller the MwC(abs)/MwC(PS) ratio (this
ratio will be hereinafter occasionally referred to as "branching degree
C"), the more preferred. The branching degree C. is preferably 0.60 or
less, more preferably 0.58 or less. The lower limit of the branching
degree C. is about 0.50.

[0049] The branched PC resin "B" must have a content of terminal hydroxyl
groups of 500 ppm by mass or more in order to produce a good foamed
blow-molded article. Since terminal hydroxyl groups of an ordinary PC
resin are end-capped with an end-capping agent in order to prevent
decomposition thereof during processing, the terminal hydroxyl group
content thereof is low. In the present invention, the branched PC resin
"B" is converted into a highly branched state by reaction with the
branching agent "D" during their melting and mixing (during step (a) and
also possibly during step (b)), as described previously. To attain this
purpose, it is necessary that the branched PC resin "B" contain a
significant amount of hydroxyl groups. When the branched PC resin "B" has
a content of terminal hydroxyl groups of 500 ppm by mass or more, it is
possible to further increase the branching degree thereof by modification
with the branching agent "D". The terminal hydroxyl group content of the
branched PC resin "B" is preferably 650 ppm by mass or more, more
preferably 800 ppm by mass or more. Since too high a terminal hydroxyl
group content may cause decomposition of the branched PC resin "B" during
melting and kneading in an extruder, it is preferred that the upper limit
of the terminal hydroxyl group content be 2,000 ppm by mass.

[0050] The linear PC resin "C" must have a content of terminal hydroxyl
groups of 250 ppm by mass or less in order to achieve the object of the
present invention. It is considered that because such a linear PC resin
"C" having a low content of terminal hydroxyl groups is not or almost not
modified with the branching agent "D" and is not or almost not bonded to
the branched PC resin "B", the PC resin "A" can exhibit low dependency of
its melt viscosity upon shear rate. From this point of view, the content
of terminal hydroxyl groups of the linear PC resin "C" is preferably 150
ppm by mass or less, more preferably 100 ppm by mass or less. The lower
limit of the terminal hydroxyl group content is 0 ppm by mass.

[0051] As used herein, the terminal hydroxyl group content of a PC resin
refers to amount of terminal hydroxyl groups as measured by colorimetric
determination using a titanium tetrachloride/acetic acid method
(Macromol. Chem., vol. 88, p 215 (1965)) and is expressed in terms of ppm
by mass of the terminal hydroxyl groups based on the mass of the PC
resin.

[0052] As used herein, the term branching agent "D" is intended to refer
to a compound having a plurality of functional groups, such as epoxy
groups and carboxyl groups, that can react with hydroxyl groups of a PC
resin. Examples of the branching agent "D" include acrylic polymers
having a plurality of functional epoxy groups; and carboxylic acid
compounds (such as carboxylic acids, carboxylic anhydrides and carboxylic
esters) having 3 or more functionalities. The acrylic polymer is
preferably a copolymer of an epoxy group-containing acrylic monomer with
a copolymerizable monomer having no epoxy group. The epoxy
group-containing acrylic monomer may be, for example, glycidyl
methacrylate. The copolymerizable monomer having no epoxy group may be,
for example, (1) a copolymerizable monomer other than acrylic monomer,
such as styrene, (2) an acrylic monomer having no epoxy group, such as
butyl acrylate and methyl methacrylate, or (3) a mixture of the above
monomers (1) and (2).

[0054] The amount of the branching agent "D" to be admixed with the PC
resins "B" and "C" cannot be specifically defined, since it is dependent
upon the kind of the PC resins "B" and "C", blending ratio between them
and kind of the branching agent (reactivity of the branching agent varies
with the kind and number of its functional groups). When an
epoxy-functional acrylic polymer having a weight average molecular weight
of 5,000 to 20,000 and an epoxy value of 1.5 meq/g or more is used as the
branching agent "D", it is preferable to use the branching agent "D" in
an amount of 0.5 to 4.5 parts by mass per 100 parts by mass of the
branched PC resin "B". The "weight average molecular weight" of the
epoxy-functional acrylic polymer as used herein refers to polystyrene
equivalent weight average molecular weight as measured by the
above-described method used for the measurement of the PC resins.

[0055] It is preferred that the foamed parison obtained in step (c) have a
polystyrene equivalent weight average molecular weight MwP(PS) of
5.0×104 to 10×104, and a weight average absolute
molecular weight MwP(abs) providing a ratio
MwP(abs)/MwP(PS) (this ratio will be hereinafter occasionally
referred to as "branching degree P") of the weight average absolute
molecular weight MwP(abs) to the weight average molecular weight
MwP(PS) of 1.0 or more (namely, very high branching degree P) for
reasons of obtaining extremely excellent foamed blow-molded article. When
the foamed parison has the above-mentioned specific molecular weight
MwP(PS) and high branching degree P, the foamed blow-molded article
obtained therefrom has especially high closed cell content and good
appearance. From this point of view, the molecular weight MwP(PS) is
more preferably 5.0×104 to 9.0×104, still more
preferably 5.0×104 to 8.5×104. In this connection,
it is to be noted that the mere fact that a foamed parison has a
molecular weight MwP(PS) of 5.0×104 to 10×104
and a branching degree P of 1.0 or more does not indicate that the foamed
parison shows good foamability. It is also important that the foamed
parison should be obtained from the PC resins "B" and "C" and branching
agent "D" as described above.

[0056] Incidentally, it is not possible to directly measure the
polystyrene equivalent weight average molecular weight MwA(PS) and
branching degree A of the PC resin "A" contained in the molten foamable
resin composition which is being extruded through a die. However, the
MwA(PS) and the branching degree A of the PC resin "A" in the molten
foamable resin composition are generally the same as MwP(PS) and the
branching degree P of a foamed parison obtained therefrom and also the
same as hereinafter described MwF(PS) and branching degree F. of the
foamed blow-molded article obtained from the foamed parison. Thus, it is
preferred that the blow-molded article have a polystyrene equivalent
weight average molecular weight MwF(PS) of 5.0×104 to
10×104, and a weight average absolute molecular weight
MwF(abs) providing a ratio MwF(abs)/MwF(PS) (this ratio
will be hereinafter occasionally referred to as "branching degree F.") of
the weight average absolute molecular weight MwF(abs) to the weight
average molecular weight MwF(PS) of 1.0 or more (namely, very high
branching degree F.) for reasons of obtaining extremely excellent foamed
blow-molded article. The foamed blow-molded article, which has the
above-mentioned specific molecular weight MwF(PS) and high branching
degree F., exhibits especially high closed cell content and good
appearance. From this point of view, the molecular weight MwF(PS) is
more preferably 5.0×104 to 9.0×104, still more
preferably 5.0×104 to 8.5×104. In this connection,
it is to be noted that the mere fact that a foamed blow-molded article
has a molecular weight MwF(PS) of 5.0×104 to
10×104 and a branching degree F. of 1.0 or more does not
indicate that the article shows good closed cell content and good
appearance. It is also important that the foamed blow-molded article
should be obtained from the PC resins "B" and "C" and branching agent "D"
as described above.

[0057] It is also preferred that the foamed blow-molded article show a
Mark-Houwink plot in which the slope S in a high molecular weight region
is 0.50 or less. As used herein, "Mark-Houwink plot" refers to a
double-logarithmic plot of intrinsic viscosity (ordinate) against
absolute molecular weight (abscissa) determined by analysis with a
GPC-RALLS-visometer system. In this plot, log(molecular weight) versus
log(intrinsic viscosity) shows a linear relationship for linear polymers.
In the case of branched polymers, the slope changes and becomes gentle on
a high molecular weight region. It is possible to evaluate the presence
of branches in a given polymer from a change of the slope. Namely, the
smaller the slope, the greater is the number of branches contained in the
polymer. In the case of a PC resin, a change in the slope occurs at a
point in a molecular weight region of between 1.5×104 and
20×104, although the point varies with the average molecular
weight of the PC resin. The above-described slope S in a high molecular
weight region is the slope of the linear region of the plot after the
slope change. The smaller the slope S, the greater is the amount of
branches and the better is the foamability of the resin and,
consequently, the better is the obtained foamed blow-molded article. From
this point of view, the slope S is more preferably 0.45 or less, still
more preferably 0.40 or less. Incidentally, linear PC resins generally
show a slope S of about 0.7, while commercially available branched PC
resins show a slope S of about 0.6.

[0058] The PC resin "A" is obtainable by melting and mixing the branched
PC resin "B", linear PC resin "C" and branching agent "D" (step a). A
method for mixing the branched PC resin "B", linear PC resin "C" and
branching agent "D" is not specifically limited. For example, the PC
resins "B" and "C" and branching agent "D" may be first melted and
kneaded to obtain a mixture (this may be hereinafter occasionally
referred to as "PC resin "X"). The PC resin "X" may be then fed to an
extruder of a blow molding device as such or after having been further
mixed with at least one of the PC resins "B" and "C" and branching agent
"D". Alternatively, the PC resins "B" and "C" and branching agent "D" may
be dry-blended together and the resulting blend may be fed to an extruder
of a blow molding device. In a further method, the PC resin "B" and
branching agent "D" may be first melted and mixed to obtain a modified PC
Resin "B". The modified PC Resin "B" thus obtained may be then
dry-blended with the PC resin "C" and the blend may be fed to an extruder
of a blow molding device. In a further alternate method, the PC resin "C"
and branching agent "D" may be first melted and mixed. The resulting
mixture may be dry-blended with the PC Resin "B", and the may be fed to
an extruder of a blow molding device. In any of the foregoing methods,
the PC resin X may be additionally added in any desired step. It is
preferred that the step (a) be performed at a temperature of about 250 to
320° C., more preferably about 260 to 300° C. for about 3
to 30 minutes, more preferably about 5 to 25 minutes.

[0059] In blow molding, since a parison is sandwiched between molds, a
parting line is generally formed on a periphery of the molded article as
a result of cutting by the molds. Protruding fins which are formed along
the parting line are removed. The fins which are produced in a large
amount may be collected and repelletized for recycling. Such fins when
produced in the blow molding process of the present invention may be
suitably used again as a raw material PC resin, since the collected fins
are formed of the PC resin "A" produced from the branched PC resin "B",
linear PC resin "C" and the branching agent "D".

[0060] In the process of the present invention, a mass ratio B:C of the
branched polycarbonate resin "B" to the linear polycarbonate resin "C"
should be 30:70 to 95:5. When the proportion of the linear polycarbonate
resin "C" is excessively small (namely when B:C ratio is greater than
95:5), it is not possible to obtain sufficient foamability improving
effect. When proportion of the linear polycarbonate resin "C" is
excessively large (namely when B:C ratio is smaller than 30:70), it is
necessary to use a large amount of the branching agent "D" and to
increase the branching degree of the branched polycarbonate resin "B",
since otherwise the foamability improving effect is not obtainable.
However, this results in an excessive increase of the molecular weight of
the branched polycarbonate resin "B" and in deterioration of the
miscibility between the highly branched polycarbonate resin "B" and the
linear polycarbonate resin "C". Thus, the use of an excessively large
amount cannot achieve the foamability improving effect. From these view
points, the mass ratio B:C of the branched polycarbonate resin "B" to the
linear polycarbonate resin "C" is preferably 40:60 to 90:10, more
preferably 50:50 to 80:20.

[0061] The melt viscosity and melt tension of the foamed blow-molded
article (the base resin that constitutes the foam of the foamed
blow-molded article), which are the same as those of the PC resin "A" at
the time it is extruded through a die for the formation of a foamed
parison, will be next described. The foamed blow-molded article
preferably has a melt viscosity of 1.5×103 to
1.0×104 Pas, more preferably 1.5×103 to
8.0×103 Pas, at 250° C. and at a shear rate of 100
sec-4, for reasons that excessive shear heat generation during
extrusion of the foamed parison from which the foamed blow-molded article
is made can be suppressed, excessive draw down of the foamed parison can
be prevented and, therefore, a foamed blow-molded article having high
thickness accuracy and high closed cell content is easily obtainable.

[0062] The "melt viscosity" refers to viscosity as measured for fully
dried PC resin sample (water content: 100 ppm by mass or less) using an
orifice having an inner diameter of 1 mm and a length of 10 mm. The
measurement may be carried out using a measuring apparatus "CAPILOGRAPH
1D" (manufactured by Toyo Seiki Srisaku-sho Ltd.).

[0063] The foamed blow-molded article preferably has a melt tension of 15
cN or higher, more preferably 17 cN or higher, at 250° C. for
reasons that breakage of cells during foaming and blow molding stages can
be effectively prevented. The upper limit of the melt tension is about 50
cN.

[0064] As used herein the term "melt tension" refers to melt tension as
measured by the following method. A cylinder having a cylinder diameter
of 9.55 mm and a length of 350 mm and an orifice having a nozzle diameter
of 2.095 mm and a length of 8.0 mm are used. With the cylinder and the
orifice set at a temperature of 230° C., a PC resin sample is
charged in a required amount in the cylinder and held therein for 4
minutes. The molten resin is then extruded in the form of a string
through the orifice at a piston speed of 10 mm/minute. The extruded
string is put on a tension-detecting pulley having a diameter of 45 mm
and is taken up on a roller while increasing the take-up speed at a
constant take-up acceleration rate such that the take-up speed increases
from 0 m/minute to 200 m/minute through a period of 4 minutes. At this
time, the maximum tension (cN) immediately before the string breaks is
measured. When the resin string does not break up to the take-up speed of
200 m/minute, then the melt tension (cN) is as measured by the take-up
operation at a constant take-up speed of 200 m/minute. It is to be noted
that the above measurement should be carried out such that inclusion of
air bubbles in the string is prevented as much as possible at the time of
extrusion of the molten resin in the string form through the orifice.

[0065] In one preferred embodiment of the process of the present
invention, the PC resins "A" thus prepared is fed to an extruder of a
blow molding device, where it is admixed with a blowing agent to obtain a
foamable molten resin composition. The foamable molten resin composition
is then extruded through a die attached to the extruder to obtain a
foamed parison in a softened state. The foamed parison is inserted
between molds and blow-molded to obtain a foamed blow-molded article.

[0066] The blowing agent to be incorporated into the foamable molten resin
composition may be a physical blowing agent, a chemical blowing agent or
a mixture of these blowing agents. Examples of the physical blowing agent
include aliphatic hydrocarbons such as propane, n-butane, isobutane,
n-pentane, isopentane, n-hexane and isohexane; alicyclic hydrocarbons
such as cyclobutane, cyclopentane and cyclohexane; halogenated
hydrocarbons such as methyl chloride, ethyl chloride,
1,1,1,2-tetrafluoroethane and 1,1-difluoroethane; alcohols such as
ethanol and methanol; ethers such as dimethyl ether, diethyl ether and
methyl ethyl ether; inorganic physical blowing agents such as carbon
dioxide, nitrogen and argon. Examples of the chemical blowing agent
include azodicarbonamide, sodium bicarbonate and a mixture of sodium
bicarbonate with citric acid. These blowing agents may used singly or in
combination of two or more thereof.

[0067] Among the above blowing agents, the use of a physical blowing agent
is preferred. It is more preferred that a physical blowing agent contain
50 to 100 mol % of carbon dioxide (the blowing agent may consist only of
carbon dioxide) because of reduced cycle time required for completing one
molding cycle and improved dimensional stability of the hollow foamed
blow-molded article. It is particularly preferred that the blowing agent
be composed only of a physical blowing agent such as carbon dioxide. A
cell controlling agent such as talc may be added to the PC resin "A". The
above-described chemical blowing agent may also used as the cell
controlling agent. The cell controlling agent is generally used in the
form of a master batch. The cell controlling agent is used in an amount
of 0.05 to 10 parts by weight per 100 parts by weight of the PC resin
"A". If desired, one or more additives such as a flame retardant, a
fluidity improver, a UV absorbing agent, an electrical conductivity
imparting agent, a colorant, a thermal stabilizer, an antioxidant and an
inorganic filler may be also suitably added to the PC resin "A".

[0068] In the process for producing a foamed blow-molded article of the
present invention, the apparent density, closed cell content and other
properties may be mainly controlled by adjustment of the using amount of
the physical blowing agent. Such properties may also be controlled by
adjustment of the discharge rate and the resin temperature at the time
the foamable molten resin composition is extruded through a die. Namely,
as the amount of the physical blowing agent increases, the average
apparent density of the foamed blow-molded article tends to decrease. The
amount of the physical blowing agent is generally properly determined in
consideration of the desired expansion ratio and the kind of the blowing
agent. When carbon dioxide is used as the blowing agent, for example, the
amount thereof is preferably 0.1 to 1 mole per 1 kg of the PC resin "A"
in order to obtain a foamed blow-molded article having an apparent
density of 0.1 to 0.8 g/cm3. The apparent density of the foamed
blow-molded article generally decreases with an increase of the discharge
rate or an increase of the resin temperature, even when the amount of the
blowing agent is held constant.

[0069] When the discharge rate is excessively high, however, cells of the
foamed parison are apt to open due to shear heat generation. On the other
hand, too slow a discharge rate will cause premature foaming in the die
and, hence, will result in formation of open cells. Even when such
premature foaming does not occur, there is still a possibility that the
resin may solidify during extrusion so that open cells are formed during
the blow molding stage. Thus, the discharge rate is generally 10 to 100
kg/hcm2.

[0070] When the resin temperature at the time the foamable molten resin
composition is extruded through a die is excessively high, problems such
as formation of open cells, deterioration of blow moldability and
phenomenon of draw down tend to occur in the foamed parison. From this
point of view, the resin temperature at the time of extrusion of the
parison is generally about 205 to 240° C., particularly preferably
210 to 230° C.

[0071] The foamed blow-molded article produced in the process of the
present invention preferably has an apparent density of 0.1 to 0.8
g/cm3 and an average wall thickness of 0.5 to 10 mm. When the
apparent density and average wall thickness of the foamed blow-molded
article are within the above ranges, the article shows a good balance
between the mechanical property (e.g., bending strength and compressive
strength), lightness in weight and heat insulation property. From this
point of view, the apparent density is more preferably 0.12 to 0.6
g/cm3, still more preferably 0.15 to 0.4 g/cm3, while the
average wall thickness is more preferably 1 to 8 mm, still more
preferably 2 to 6 mm. As used herein, "apparent density" of the foamed
blow-molded article refers to values calculated by dividing the weight
(g) of the foamed blow-molded article sample by the volume (cm3)
thereof which is measured by, for example, immersing the sample in water.

[0072] The term "average wall thickness" of the foamed blow-molded article
as used herein refers to thickness as measured by the following method.
The blow-molded article is cut by a plane perpendicular to an axial
(longitudinal) direction thereof at seven (7) positions including a first
position near one end thereof, a second position near the other end
thereof, and five positions which divide the length between the first and
second positions into six nearly equal lengths. Each of the
cross-sections thus obtained in the seven different positions is measured
for the wall thickness at eight (8) locations which are nearly equally
spaced from each other along the perimeter thereof. The average wall
thickness is the arithmetic mean of the fifty six (56) measured thickness
values. In measuring the wall thickness, each of the cross sections is
enlarged using a microscope or the like. On the enlarged image, the wall
thickness (length in the thickness direction) is measured at average
thickness locations. The wall thickness is calculated by dividing the
measured value by the magnification of the enlarged image.

[0073] It is preferred that the foamed blow-molded article have a
variation coefficient Cv of its wall thickness of 50% or less. A small
variation coefficient Cv means that the foamed blow-molded article has
uniform wall thickness. When the wall thickness of the foamed blow-molded
article is not uniform, such an article has thin walled portions that
have relatively weak mechanical strength. In designing a foamed
blow-molded article which satisfies the desired strength and heat
insulation property, it is generally necessary to determine the average
thickness thereof with due consideration of thin walled portions thereof.
Therefore, when the wall thickness of the foamed blow-molded article is
not uniform, the average wall thickness must be increased so that it
becomes difficult to sufficiently achieve a reduction of the weight
thereof. Thus, a foamed blow-molded article that has a small variation
coefficient Cv is excellent in uniformity of mechanical strength and heat
insulation property, and, therefore, is able to achieve a reduction of
the weight thereof. For the above reasons, the variation coefficient Cv
of the foamed blow-molded article is desired to be as small as possible.
In particular, the variation coefficient Cv is more preferably 40% or
less, even more preferably 30% or less, still more preferably 25% or
less, particularly preferably 20% or less. The process of the present
invention enables to produce foamed blow-molded articles having excellent
uniformity in wall thickness over a wide range of its apparent density.

[0074] The term "variation coefficient Cv" of the wall thickness of the
foamed blow-molded article as used herein is defined by the percentage of
the standard variation V (mm) of the thickness of the foamed blow-molded
article relative to the average thickness T (mm) thereof and represents a
degree of variation from the average value. The standard variation V of
the thickness of the foamed blow-molded article is calculated according
to the following formula (1):

V={Σ(Ti-Tav)2/(n-1)}1/2 (1)

wherein Ti is a measured thickness value of each of the
above-described 56 locations, Tav is the above-described average
thickness, n is the number of the measurement (namely, 56) and Σ
means a sum of (Ti-Tav)2 calculated for respective
measured values. Thus, the variation coefficient Cv can be determined
from the following formula (2):

Cv(%)=(V/Tav)×100 (2)

[0075] The foamed blow-molded article produced by the process of the
present invention preferably has a closed cell content of 60% or more,
more preferably 70% or more, particularly preferably 80% or more. When
the closed cell content is within the above range, excellent mechanical
strength such as bending strength and compressive strength that is
inherent to the PC resin may be attained even when the foamed blow-molded
article is rendered to be light weight by increasing its expansion ratio
and by reducing its wall thickness.

[0076] As used herein, the closed cell content (%) refers to values
calculated by the formula (3) below upon determining the true volume
Vx according to Procedure C of ASTM D-2856-70 (reapproved 1976). In
this case, when the required volume cannot be obtained from one sample,
two or more samples may be combined together to get as close the required
volume as possible.

Closed cell content
(%)=(Vx-Va(ρf/ρs))×100/(Va-Va-
(ρf/ρs)) (3)

[0077] wherein Vx represents a true volume (cm3) of the
specimen, which corresponds to a sum of a volume of the resin
constituting the specimen and a total volume of closed cells in the
specimen,

[0078] Va represents the apparent volume (cm3) of the specimen
which is calculated from the outer dimension thereof,

[0079] ρf represents the apparent density (g/cm3) of the
specimen, and

[0080] ρs represents the density (g/cm3) of the base resin
constituting the specimen.

[0081] The foamed blow-molded article produced by the process of the
present invention preferably has an average cell diameter of 0.1 to 1 mm,
more preferably 0.1 to 0.8 mm. The foamed blow-molded article, which has
an average cell diameter within the above range, can sufficiently exhibit
the excellent mechanical strength such as bending strength and
compressive strength that is inherent to the PC resin. As used herein,
the "average cell diameter" of the foamed blow-molded article refers to
mean cell diameter as measured in accordance with ASTM D3576-77. More
specifically, a cross-section of the foamed molded article is magnified
and projected. A straight line is drawn on the projected image. The
number of cells that intersect this line is counted. The value computed
by dividing the length of the straight line by the count of the number of
cells is further divided by 0.616 to obtain an average cell diameter.
Such a measurement is carried out for determining the average cell
diameter in each of the extrusion direction (generally longitudinal
direction), peripheral direction and thickness direction of the foamed
blow-molded article. The arithmetic mean of the average cell diameters in
these three directions represents the average cell diameter of the foamed
blow-molded article.

[0082] The process of the present invention enables to easily produce
foamed blow-molded articles having a high closed cell content over a wide
range of its apparent density. With the conventional processes, it has
been difficult to produce a foamed blow-molded article having a high
closed cell content and a high expansion ratio (for example, an apparent
density of less than 0.2 g/cm3). With the process of the present
invention, on the other hand, it is possible to produce a foamed
blow-molded article having a closed cell content of 60% or higher and a
low apparent density of less than 0.2 g/cm3. Further, with the
conventional process, a reduction of the average cell diameter causes an
increase of the open cell structure because of excessive reduction of the
cell wall thickness. In contrast, the process of the present invention
makes it possible to produce a foamed blow-molded article having a closed
cell content of 60% or higher over a wide range of its apparent density,
even when the average cell diameter is as small as 0.1 to 1 mm.

EXAMPLES

[0083] The following examples and comparative examples will further
illustrate the present invention. Raw materials used in the examples and
comparative examples and methods for evaluating the foamed blow-molded
articles obtained in the examples and comparative examples are first
described below.

(1) Raw Materials

[0084] (i) PC resin

[0085] Tables 1 and 2 show 6 types of raw material PC resins used (PC1,
PC2 and PC4 to PC7). PC1 is a branched PC resin (NOVAREX M7027BF
manufactured by Mitsubishi Engineering-Plastics Corporation). PC2 is a
branched PC resin (TARFLON IB2500 manufactured by Idemitsu Kosan Co.,
Ltd.). PC4 to PC7 are linear PC resins (IUPILON H-4000, IUPILON H-3000,
IUPILON S-3000 and IUPILON E-2000, respectively, manufactured by
Mitsubishi Engineering-Plastics Corporation). Also used were 4 types of
raw material PC resins (PC11, PC12, PC21 and PC22) shown in Table 3, in
which PC 11 is a PC resin recycled from Example 1 and PC 12 is a PC resin
recycled from Example 3. PC 21 is a PC resin obtained by melting and
kneading a mixture of PC1 and a branching agent (described hereinafter)
with a mixing ratio (by mass) of PC1 to the branching agent of 100:2.1
using a twin screw extruder set at 280° C., and pelletizing the
kneaded mixture. PC22 is a PC resin obtained by melting and kneading a
mixture of PC1 and a branching agent (described hereinafter) with a
mixing ratio (by mass) of PC1 to the branching agent of 100:3.0 using a
twin screw extruder set at 280° C., and pelletizing the kneaded
mixture. The terminal hydroxyl group content (ppm by mass) shown in
Tables 1 to 3 is as determined by arbitrarily sampling three specimens
from the pellets of the raw material PC resin and measuring the terminal
hydroxyl group content of each of the specimens according to the method
described previously. The arithmetic mean of the terminal hydroxyl group
contents of the three samples is the terminal hydroxyl group content of
the raw material PC resin. The slope S shown in Tables 1 to 3 is the
slope of the hereinafter described Mark-Houwink plot.

[0086] As a branching agent, an acrylic polymer having epoxy groups
(ARUFON UG-4035 manufactured by Toagosei Co., Ltd.; epoxy value: 1.8
meq/g; weight average molecular weight: 11,000) was used. The epoxy value
(meq/g) is the millimole number of the epoxy group per 1 g of the
branching agent and is equal to the number obtained by dividing 1000 by
the epoxy equivalent (g/eq) of the branching agent. The epoxy equivalent
was measured according to JIS K7236:2001.

[0090] According to the measuring methods described previously, the weight
average absolute molecular weight, polystyrene equivalent weight average
molecular weight and slope S of foamed blow-molded articles were
measured. These weight average molecular weights were determined using an
analysis software EzChromElite (Scientific Software Inc.). The
polystyrene equivalent weight average molecular weight was determined by
gel permeation chromatography using UV (ultraviolet spectrophotometer) as
a detector. The polystyrene equivalent weight average molecular weight is
a polystyrene equivalent value obtained from a calibration curve prepared
using linear polystyrene as a standard polymer. In the measurement of the
weight average absolute molecular weight and polystyrene equivalent
weight average molecular weight of a foamed blow-molded article, three
specimens were sampled from the blow-molded article at three positions,
i.e. near both end portions and middle portion in the longitudinal
(extrusion) direction of the article. The arithmetic mean of the measured
values of the three specimens represents the weight average absolute
molecular weight and polystyrene equivalent weight average molecular
weight of the foamed blow-molded article. In Tables 6-1 and 7-1,
described hereinafter, the weight average absolute molecular weight and
polystyrene equivalent weight average molecular weight of the foamed
blow-molded article are indicated as Mw(abs) and Mw(PS), respectively. A
foamed parison which had not yet been subjected to blow molding was
sampled and measured for its Mw(abs) and Mw(PS). It was revealed that
Mw(abs) and Mw(PS) of the foamed parison are the same as Mw(abs) and
Mw(PS), respectively, of the foamed blow-molded article which was
obtained from the similar foamed parison. Incidentally, the
above-described method for the measurement of the weight average absolute
molecular weight and polystyrene equivalent weight average molecular
weight of a foamed blow-molded article also applies to that of raw
material PC resins. In the case of raw material PC resins, three
specimens are arbitrarily sampled from the pellets of a raw material PC
resin. The arithmetic mean of the measured values of the three specimens
represents the weight average absolute molecular weight and polystyrene
equivalent weight average molecular weight of the raw material PC resins
and are shown in Tables 1 to 3. In Tables 1 to 3, the weight average
absolute molecular weight and polystyrene equivalent weight average
molecular weight of the raw material PC resin are indicated as Mw(abs)
and Mw(PS), respectively.

[0091] (ii) Melt Tension and Melt Viscosity

[0092] The melt tension and melt viscosity of foamed blow-molded articles
were measured by the method described previously using "CAPILOGRAPH 1D"
(manufactured by Toyo Seiki Seisaku-sho Ltd.). Specimens were measured
after having been dried in a recirculation type hot air oven at
120° C. for 12 hours. In the measurement of the melt tension and
melt viscosity of a foamed blow-molded article, three specimens were
sampled from the blow-molded article at three positions, i.e. near both
end portions and middle portion in the longitudinal (extrusion) direction
of the article. Each of the specimens was dried in a recirculation type
hot air oven at 120° C. for 12 hours, heat-pressed at 10 MPa for
defoaming, cut into a suitable size and then measured for the melt
tension and melt viscosity. The arithmetic mean of the measured values of
the three specimens represents the melt tension and melt viscosity of the
foamed blow-molded article.

(iii) Apparent Density

[0093] The apparent density of a foamed blow-molded article was calculated
by dividing the weight (g) of the foamed blow-molded article by the
volume (cm3) thereof which is measured by immersing the foamed
blow-molded article in water.

[0094] The average wall thickness and variation coefficient of wall
thickness Vc were measured by the method described previously.

(v) Average Cell Diameter

[0095] In the measurement of the average cell diameter of a foamed
blow-molded article, three specimens were sampled from the blow-molded
article at three positions, i.e. near both end portions and middle
portion in the longitudinal (extrusion) direction of the article. Each of
the three specimens was measured for its average cell diameter by the
method described previously according to ASTM D3576 in each of the
longitudinal, peripheral and thickness directions thereof. The arithmetic
mean of the measured values represents the average cell diameter of the
foamed blow-molded article.

[0096] (vi) Closed Cell Content

[0097] In the measurement of the closed cell content of a foamed
blow-molded article, three specimens were sampled from the blow-molded
article at three positions, i.e. near both end portions and middle
portion in the longitudinal (extrusion) direction of the article. Each of
the three specimens was measured for its closed cell content by the
method described previously according to Procedure C of ASTM D-2856-70
(reapproved 1976). The arithmetic mean of the measured values represents
the closed cell content of the foamed blow-molded article.

(vii) Appearance

[0098] Each of the foamed blow-molded articles was evaluated for its
appearance according to the following criteria:

Good: No surface roughness was observed on the surface of the foamed
blow-molded article Poor: Significant surface roughness was observed on
the surface of the foamed blow-molded article

Examples 1 to 17 and Comparative Examples 1 to 10

[0099] A molding device having two separable mold halves for forming an
air duct having a maximum length of 650 mm, a maximum width of 150 mm and
a maximum thickness of 70 mm was used.

[0100] Raw material PC resins (kinds and amounts are shown in Tables 4 and
5), a branching agent (amount is shown in Tables 4 and 5; the symbol "-"
in Tables 4 and 5 indicates that no branching agent was added) and talc
(HI-Filler #12) as a cell controlling agent were supplied to an extruder
having a diameter of 65 mm and kneaded in the extruder set at a
temperature of 280° C. to form a molten mixture. The amount of the
branching agent shown in Tables 4 and 5 is expressed in terms of parts by
mass per 100 parts by mass of the raw material PC resins. The amount of
talc was 0.05 part by mass per 100 parts by mass of a total amount of the
raw material PC resins and the branching agent in all of Examples and
Comparative Examples except for Comparative Examples 1 and 4 in which
talc was used in an amount of 0.1 part by mass per 100 parts by mass of a
total amount of the raw material PC resins and the branching agent.
Carbon dioxide (CO2) as a blowing agent was supplied under pressure
to an intermediate portion of the kneader and kneaded together with the
above molten mixture to form a foamable molten resin composition. The
amount of CO2 was 0.34 mole per 1 kg of the molten mixture in all of
Examples and Comparative Examples except for Example 2 in which CO2
was used in an amount of 0.23 mole/kg. The foamable molten resin
composition was cooled to a temperature suited for foaming and fed into
an accumulator directly connected to the extruder and provided at its end
with a circular die having a diameter of 90 mm and a lip clearance of 1.8
mm. The foamable molten resin composition was then extruded through the
circular die into an ambient pressure zone and allowed to foam to form a
foamed parison.

[0101] While blowing pre-blow air into the foamed parison, the foamed
parison was clamped between the two mold halves disposed just beneath the
die. A blow pin was then introduced into the foamed parison. Blow air was
blown into the foamed parison from the blow pin, while evacuating the
space between the outer surface of the foamed parison and the inner
surface of the molds through vents provided in the molds, to press the
outer surface of the foamed parison against the inner surface of the
molds and to blow-mold the foamed parison. After cooling, the molds were
opened and the blow-molded product was taken out of the molds. Protruding
fins were removed from the blow-molded product to give a foamed
blow-molded article.

[0102] Parison forming conditions including the discharge amount (kg/h) of
the foamable molten resin composition, the discharge rate (kg/hcm2)
of the foamable molten resin composition per unit area of the die lip and
the surface temperature (° C.) of the foamed parison are
summarized in Tables 4 and 5. The surface temperature of the foamed
parison was measured before carrying out the blow molding of the foamed
parison. Thus, the foamed parison, immediately after having been extruded
from the die, was measured for its surface temperature at a position 100
mm below the tip of the die using an IR thermometer (Model 8700II
manufactured by Sato Keiryoki Mfg. Co., Ltd.). The distance between the
surface of the parison and the thermometer was 50 mm.

[0104] The foamed blow-molded article obtained by the process of the
present invention has excellent heat insulating property, heat resistance
and mechanical strengths and, therefore, may be advantageously used for
various applications such as automobile parts, electric or electronic
parts, packaging materials and receptacles.

[0105] The invention may be embodied in other specific forms without
departing from the spirit or essential characteristics thereof. The
present embodiments are therefore to be considered in all respects as
illustrative and not restrictive, the scope of the invention being
indicated by the appended claims rather than by the foregoing
description, and all the changes which come within the meaning and range
of equivalency of the claims are therefore intended to be embraced
therein.